1. Field of the Invention
The present invention relates to a liquid-discharge head for performing recording on a recording medium by discharging droplets of a liquid, such as ink, or the like. More particularly, the invention relates to a liquid discharge head for performing ink-jet recording.
2. Description of the Related Art
An ink-jet recording method is one of so-called non-impact recording methods. In the ink-jet recording method, noise generated during recording is negligibly small, and high-speed recording can be performed. Furthermore, recording can be performed on various recording media. For example, on so-called ordinary paper, ink is fixed without requiring particular processing, and a very precise image can be inexpensively obtained. Because of such features, the ink-jet recording method has been rapidly spreading recently not only for printers, serving as peripheral apparatuses of computers, but also as recording means for copiers, facsimile apparatuses, word processors, and the like.
Generally utilized ink discharge methods of the ink-jet recording method include a method of using electrothermal transducers, such as heaters or the like, as discharge-energy generation elements used for discharging ink droplets, and a method of using piezoelectric elements. Each of these methods can control discharge of ink droplets by an electric signal. The principle of the ink discharge method using electrothermal transducers consists in causing ink near an electrothermal transducer to instantaneously boil by applying a voltage to the electrothermal transducer, and discharging an ink droplet at a high speed by an abrupt bubble pressure generated by a phase change of ink at boiling. The method of discharging ink using piezoelectric elements consists in discharging ink droplets by a pressure generated during displacement of a piezoelectric element caused by application of a voltage to the piezoelectric element.
The ink discharge method using electrothermal transducers has, for example, the features that it is unnecessary to provide a large space for disposing discharge-energy generation elements, the structure of a recording head is simple, and nozzles can be easily integrated. However, this method has, for example, the peculiar problems that the volume of ink droplets to be ejected changes due to storage of heat generated by the electrothermal transducers within the recording head, cavitation produced by disappearance of bubbles adversely influences the electrothermal transducers, and the discharge characteristics of ink droplets and the image quality are adversely influenced by bubbles of air dissolved within the ink that remains within the recording head.
In order to solve these problems, Japanese Patent Application Laid-Open (Kokai) Nos. 54-161935 (1979), 61-185455 (1986), 61-249768 (1986) and 4-10941 (1992) disclose ink-jet recording methods and recording heads. In the ink-jet recording methods that have been disclosed in the above-described publications, a bubble generated by driving an electrothermal transducer is caused to communicate with external air. By adopting such ink-jet recording methods, for example, it is possible to stabilize the volume of a traveling ink droplet, discharge an ink droplet containing a very small amount of ink at a high speed, improve the durability of a heater by preventing cavitation generated during disappearance of a bubble, and easily obtain a more precise image. In the above-described publications, in order to cause a bubble to communicate with external air, a configuration is described in which the shortest distance between an electrothermal transducer for generating a bubble in ink, and a discharge port, serving as an opening for discharging ink, is greatly reduced compared with conventional configurations.
The configuration of a recording head of this type will now be described. The configuration includes an element substrate on which electrothermal transducers for discharging ink are provided, and a channel-configuration substrate (also termed an “orifice substrate”) for providing ink channels by being connected to the element substrate. The channel-configuration substrate includes a plurality of nozzles where ink flows, a supply chamber for supplying these nozzles with ink, and a plurality of discharge ports, serving as nozzle-distal-end openings for discharging ink droplets. The nozzle includes a bubble generation chamber for generating a bubble by a corresponding one of the electrothermal transducers, and a supply channel for supplying the bubble generation chamber with ink. The element substrate includes the electrothermal transducers at positions corresponding to the bubble generation chambers. The element substrate also includes a supply port for supplying the supply chamber with ink from a back surface opposite to a main surface contacting the channel-configuration substrate. The channel-configuration substrate includes discharge ports at positions facing corresponding ones of the electrothermal transducers on the element substrate.
In the recording head having the above-described configuration, ink supplied from the supply port into the supply chamber is supplied along each of the nozzles, and is filled within the bubble generation chamber. The ink filled within the bubble generation chamber is caused to travel in a direction substantially orthogonal to the main surface of the element substrate by a bubble generated by film boiling by the electrothermal transducer, and is discharged from the discharge port as an ink droplet (a head of this type is hereinafter termed a “side-shooter-type ink-jet head”).
In such a side-shooter-type ink-jet head, when discharging an ink droplet, ink filled within the bubble generation chamber travels separately toward the discharge port side and the supply channel side due to a bubble generated within the bubble generation chamber. At that time, part of the pressure due to bubble generation in the ink is applied toward the supply channel side, or a pressure loss is generated due to friction with the inner wall of the discharge port. This phenomenon adversely influences ink discharge, and is more pronounced as the amount of ink contained in the discharged ink droplet is smaller (i.e., as the volume of the discharged droplet is smaller). That is, when the discharge diameter is reduced in order to reduce the volume of the discharged ink droplet, the fluid resistance of the discharge port greatly increases to reduce the flow rate toward the discharge port and increase the flow rate toward the supply channel, thereby reducing the discharge speed of the ink droplet.